1. Field of the Invention
This invention relates to automotive brake systems, and more specifically, to an improvement in automotive parking brake systems.
2. Description of the Prior Art
It is generally desirable that a parking brake be actuated when an automotive vehicle is stopped in order to minimize the damage from a possible rear-end collision, and application of the parking brake is required particularly upon stopping on a slope so that the vehicle will be prevented from rolling down the slope even when the main or foot brake is released. However, the conventional type of parking brake actuated by manual operation is very troublesome to operate every time the vehicle is stopped and started and is liable to cause the operator increased fatigue. In addition, with such a conventional parking brake, it has been frequently experienced that brake drag and/or engine stall are caused when the vehicle is inadvertently started without releasing the brake.
In order to cope with the above-described problems, various proposals have hitherto been made for automating the operation of the parking brake. For example, Japanese Unexamined Utility Model Publication No. 48(1973)-21329 relates to an invention entitled "Device for Controlling a Side Brake in an Automobile" which is characterized by an actuator means adapted to be operated by an actuation signal, which is developed upon depression of the foot-brake pedal during stopping of the vehicle, to actuate a side or parking brake, and a brake release means adapted to be operated by a release signal, which is issued upon depression of the accelerator pedal under application of the side brake, to release the latter. Also, disclosed in Japanese Unexamined Utility Model Publication No. 54(1979)-105429 is an invention named "Side Brake Control Device" in which current is supplied to a motor for actuating a side brake in response to the respective actuations of a foot-brake switch responsive to the depressionof the foot brake, and a pushbutton switch adapted to be operated upon actuation of the side brake, the supply of current to the motor being stopped in response to the depression of the accelerator pedal or the clutch pedal. Further, according to Japanese Unexamined Patent Publication No. 55(1980)-140634, there is shown a "System for Automatically Releasing a Parking Brake in an Automobile" which comprises a parking-brake detecting means for detecting the application of a parking brake, an accelerator-pedal detecting means for detecting the depression of the accelerator pedal, a shift-position detecting means for detecting the shift position of the transmission, and a brake-releasing means operable to release the parking brake in response to signals from the above-mentioned respective means.
In accordance with the teachings of the above prior art, the aforementioned problems encountered in the manually-operated parking brake can be overcome, but on the other hand, there is another problem as described below. Namely, application and release of a parking brake must intrinsically be effected in an appropriate manner depending on whether the road on which the vehicle is stopped is flat or sloped, or depending on the gradient of the road, but none of the prior art devices as referred to above is able to control the operation of the parking brake in accordance with the gradient of the road. As a result, there arises, for example, a problem that an automobile, when stopped on a steep slope, may start to move down the slope owing to an insufficient brake force of the parking brake, or the automobile may roll back down the slope due to premature release of the parking brake upon starting on an uphill grade.